Treatment of shoulder dysfunction using a percutaneous intramuscular stimulation system

ABSTRACT

A method of treating shoulder dysfunction involves the use of a percutaneous, intramuscular stimulation system. A plurality of intramuscular stimulation electrodes are implanted directly into select shoulder muscles of a patient who has suffered a disruption of the central nervous system such as a stroke, traumatic brain injury, spinal cord injury or cerebral palsy. An external microprocessor based multi-channel stimulation pulse train generator is used for generating select electrical stimulation pulse train signals. A plurality of insulated electrode leads percutaneously, electrically interconnect the plurality of intramuscular stimulation electrodes to the external stimulation pulse train generator, respectively. Stimulation pulse train parameters for each of the stimulation pulse train output channels are selected independently of the other channels. The shoulder is evaluated for subluxation in more than one dimension. More than one muscle or muscle group is simultaneously subjected to a pulse train dosage. Preferably, the at least two dosages are delivered asynchronously to two muscle groups comprising the supraspinatus in combination with the middle deltoid, and the trapezious in combination with the posterior deltoid.

RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/867,396filed 14 Jun. 2004, now abandoned which is a divisional of patentapplication Ser. No. 10/138,791, filed 3 May 2002, now U.S. Pat. No.6,845,271, which is a continuation-in-part of patent application Ser.No. 09/862,156 filed 21 May 2001, now abandoned which is a continuationof application Ser. No. 09/089,994 filed 3 Jun. 1998, now abandoned.This application is also related to application Ser. No. 09/755,871,filed 6 Jan. 2001, now abandoned, which claims the benefit ofprovisional application Ser. No. 60/174,886 filed Jan. 7, 2000, all ofwhich are incorporated herein by reference.

FIELD OF INVENTION

The present invention relates to the art of therapeutic neuromuscularstimulation. It finds particular application for use by human patientswho are paralyzed or partially paralyzed due to cerebrovascularaccidents such as stroke or the like. The invention is useful forretarding, preventing muscle disuse atrophy and even improving muscularcondition, maintaining or improving extremity range-of-motion,facilitating voluntary motor function, relaxing spastic muscles, andincreasing blood flow to select muscles of the shoulder. Additionalbenefits of the invention may include improved alignment and decreasedpain.

BACKGROUND OF THE INVENTION

The invention is particularly useful for the treatment of shoulderdysfunction. An estimated 555,000 persons are disabled each year in theUnited States of America by cerebrovascular accidents (CVA) such asstroke. Many of these patients are left with partial or completeparalysis of an extremity including for example, hemiplegic subluxation(incomplete dislocation) of the shoulder joint. This is a commonoccurrence and has been associated with chronic and debilitating painamong stroke survivors. In stroke survivors experiencing shoulder pain,motor recovery is frequently poor and rehabilitation is impaired. Thus,the patient may not achieve his/her maximum functional potential andindependence. Therefore, prevention and treatment of subluxation instroke patients is a priority.

There is a general acknowledgment by healthcare professionals of theneed for improvement in the prevention and treatment of shouldersubluxation. Conventional intervention includes the use of orthoticdevices; such as slings and supports, to immobilize the joint in anattempt to maintain normal anatomic alignment. The effectiveness ofthese orthotic devices varies with the individual. Also, manyauthorities consider the use of slings and arm supports to becontroversial or even contraindicated because of the potentialcomplications from immobilization including disuse atrophy and furtherdisabling contractures.

Surface, (i.e., transcutaneous) electrical muscular stimulation has beenused therapeutically for the treatment of shoulder subluxation andassociated pain, as well as for other therapeutic uses. Therapeutictranscutaneous stimulation has not been widely accepted in generalbecause of stimulation-induced pain and discomfort, poor musclesselectivity, and difficulty in daily management of electrodes, whichnecessitates a highly specialized clinician for treatment. In additionto these electrode-related problems, commercially available stimulatorsare relatively bulky, have high-energy consumption, and use cumbersomeconnecting wires.

In light of the foregoing deficiencies, transcutaneous stimulationsystems are typically limited to two stimulation output channels. Theelectrodes mounted on the surface of the patient's skin are not able toselect muscles to be stimulated with sufficient particularity and arenot suitable for stimulation of the deeper muscle tissue of the patientas required for effective therapy. Any attempt to use greater than twosurface electrodes on a particular region of a patient's body is likelyto result in suboptimal stimulation due to poor muscle selection.Further, transcutaneous muscle stimulation via surface electrodescommonly induces pain and discomfort.

Studies suggest that conventional interventions are not effective inpreventing or reducing long term pain or disability. Therefore, it hasbeen deemed desirable to develop a therapy for the treatment of shoulderdysfunction which involves the use of a percutaneous, (i.e., through theskin,) neuromuscular stimulation system having implanted, intramuscularstimulation electrodes connected by percutaneous electrodes leads to anexternal and portable pulse generator.

SUMMARY OF THE INVENTION

In accordance with the first aspect of the present invention, a therapyinvolves therapeutic electrical stimulation of select shoulder musclesof a patient. The therapy includes the implantation of a plurality ofintramuscular stimulation electrodes directly into selected shouldermuscles of a patient near the muscle motor point. This avoidsstimulation of cutaneous nociceptors; requires lower stimulusintensities and avoids uncomfortable stimulation of adjacent non-targetmuscles. The electrodes are addressed using an externalbattery-operated, microprocessor-based stimulation pulse traingenerator, which generates select electrical stimulation pulse trainsignals. Preferably, the pulse train generator is portable and inparticular is miniaturized to a convenient size. This pulse traingenerator includes a plurality of electrical stimulation pulse trainoutput channels connected respectively to the plurality of percutaneouselectrode leads. Stimulation pulse train parameters are selected foreach of the stimulation pulse train output channels independently of theother channels. Muscle selection was determined generally bythree-dimensional radiographic evaluation of a number of patients alongwith selective stimulation of all of the shoulder muscles. Ultimately itwas determined that a preferred therapy involved asynchronousstimulation of more than one muscle group and more preferably with afirst muscle group being the supraspinstus in combination with themiddle deltoid and a second muscle group being the trapezious incombination with the posterior deltoid. The stimulation pulse trainparameters or regiment or dosage include at least pulse amplitude andpulse width or duration for stimulation pulses of the stimulation pulsetrain, and an interpulse interval between successive pulses of thestimulation pulse train defining a pulse frequency.

Advantageously, the therapy involves the asynchronous stimulation ofmore than one muscle or muscle group. This asynchronous stimulationinvolves intermittent periods of stimulation and rest with differentpulse train envelope delivered to the multiple sites but not in asynchronized dose. Thus, one muscle or muscle group may be resting whileanother muscle or muscle group may be subjected to stimulation. In thesimplest case, these two dosages are the same but offset in time. Withthe therapy of the present invention more than one stimulation cycle isdelivered at a point in time so that a first cycle may be delivered to afirst muscle or muscle group with a second muscle or group undergoing asecond stimulation cycle (which can be a straight, low-level stimulationor a cycle having a different profile, or can be the same cycle appliedat a different point in time). In general, the electrical stimulatorsinclude means for generating stimulation pulse train signals with theselected pulse train parameters on each of the plurality of stimulationpulse train output channels so that stimulus pulses of the pulse trainsignals having the select stimulation pulse train parameters passbetween the intramuscular electrodes respectively connected to thestimulation pulse train output channels and a reference electrode.

In accordance with another aspect of the invention, a method ofstimulating select shoulder muscle tissue of a patient includesprogramming a patient external stimulation pulse generator with at leastone stimulation pulse train session including at least one stimulationcycle (and preferably at least two stimulation cycles) defining astimulation pulse train envelope for a plurality of stimulation pulsetrain output channels. Each envelope is defined by at least a ramp-upphase of a first select duration wherein pulses of a stimulus pulsetrain progressively increase in charge, a hold phase of a second selectduration wherein pulses of the stimulus pulse train are substantiallyconstant charge, and a ramp-down phase of a third select durationwherein pulses of the stimulus pulse train progressively decrease incharge. During a second hold phase there is no stimulus delivered andthe muscles are allowed to relax or rest. In accordance with theinvention, two muscle groups are subjected to a first and a secondstimulation cycles so that one set of muscles is stimulated during therest cycle of the second set of muscles. This inhibits the shoulder fromslipping back into misalignment during the rest portion of the cycle. Aplurality of intramuscular electrodes are implanted into select shouldermuscle tissue of the patient and electrically connected by percutaneouselectrode leads to the plurality of output channels, respectively, ofthe pulse train generator. On each of said plurality of stimulationoutput channels and in accordance with a respective envelope,stimulation pulse train signals are generated with the generator so thatthe select muscle tissue of the patient is stimulated in accordance withthe at least one stimulation cycle.

Further in accordance, one advantage of the present invention is theprovision of a therapeutic percutaneous intramuscular stimulation systemthat retards or prevents muscle disuse atrophy, maintains musclerange-of-motion, facilitates voluntary motor function, relaxes spasticmuscles, and increases blood flow in selected muscles.

Another advantage of the present invention is that it provides atherapeutic muscular stimulation system that uses intramuscular, ratherthan skin surface (transcutaneous) electrodes to effect musclestimulation of select shoulder muscles.

Yet another advantage of the present invention is that the treatmentdosage or regiment, which is prescribed may be tailored to suitindividual needs and selectively varied even during the course oftreatment. For example, the stimulus may be titrated at the onset toavoid pain and unwanted joint movement (such as for example, activeelbow flexion during biceps stimulation).

In a further embodiment of the invention, a method of therapy isprovided for treatment of shoulder dysfunction (such as subluxation)which comprises the steps of: 1) radiographic evaluation of theshoulder, in at least two planes (preferably the subluxation isevaluated in 3-dimensions); 2) percutaneous implantation of two or moreelectrodes, so as to contact a muscle or nerve, the electrode being inelectrical communication with a pulse train generator; and 3) actuationof the pulse train generator in accordance with a regiment or prescribeddosage to cause stimulation of the muscle or nerve using the electrodes.The regiment or course of treatment may be a pre-defined course oftreatment based on a stimulation pattern, which has been stored in ahost computer or integral microprocessor, which can be used to addressthe pulse train generator. Preferably, the regiment will includeindividual sessions having a ramped profile and including intermittentstimulation activation of the electrode or electrodes with periods ofrest. Preferably, the treatment of shoulder subluxation involvesimplantation of one or more electrodes into the superspinatus as well asinto the posterior, middle and anterior deltoids; into thecoracolbrachialis; into the biceps and triceps longhead. Even morepreferably the treatment accounts for shoulder relocation in threedimensions with a focus on stimulation of all heads of the deltoid, thecoracobrachialis, the biceps and the triceps longhead. Modulation of thestimulus may require precise muscle activation to balance againstagonist and antagonist activity to avoid undesirable joint translationand rotation.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take form in various components and arrangements ofsteps. The drawings are only for purposes of illustrating preferredembodiments, and are not to be construed as limiting the invention.

FIG. 1A is a front elevational view of a portable, programmablestimulation pulse train generator in accordance with the presentinvention;

FIG. 1B-1D are top, bottom, and right-side elevational views of thestimulation pulse train generator of FIG. 1A;

FIG. 2 illustrates a preferred intramuscular electrode and percutaneouselectrode lead;

FIG. 3 graphically illustrates the stimulation paradigm of thepercutaneous intramuscular stimulation system in accordance with thepresent invention; and

FIG. 4 graphically illustrates the preferred stimulation paradigm;

FIG. 5 is a graphic illustration of the results of the study of Example1;

FIG. 6 is a second graphic illustration of the results of the study ofExample 1;

FIG. 7 is a graphic illustration of the results of the study of Example2;

FIG. 8 is a second graphic illustration of the results of the study ofExample 2;

FIG. 9 is a third graphic illustration of the results of the study ofExample 2;

FIG. 10 is a fourth graphic illustration of the results of the study ofExample 2;

FIG. 11 is a fifth graphic illustration of the results of the study ofExample 2; and

FIG. 12 is a sixth graphic illustration of the results of the study ofExample 2.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIGS. 1A-1D, a percutaneous, intramuscular stimulationsystem is shown which can be used with the method of treating shouldersin accordance with the present invention. The stimulator includes anelectrical stimulation pulse generator 10. The pulse generator 10includes a lightweight, durable plastic housing 12 fabricated from asuitable plastic or the like. The case 12 includes a clip 14 that allowsthe pulse generator 10 to be releasably connected to a patient's belt,other clothing, or any other convenient location. The case 12 alsoincludes a releasable battery access cover 16.

For output of visual data to a patient or clinician operating thestimulation system, a visual display 20 is provided. The display 20 ispreferably provided by a liquid crystal display, but any other suitabledisplay means may alternatively be used. An audio output device, such asa beeper 22 is also provided.

For user control, adjustment, and selection of operational parameters,the stimulation pulse generator 10 includes means for input of data.Preferably, the pulse generator 10 includes an increment switch 24, adecrement switch 26, and a select or “enter” switch 28. The incrementand decrement switches 24, 26 are used to cycle through operationalmodes or patterns and stimulation parameters displayed on the display20, while the select switch 28 is used to select a particular displayedoperational pattern or stimulation parameter. The select switch 28 alsoacts as a power on/off toggle switch.

For output of electrical stimulation pulse train signals, the pulsetrain generator 10 includes an external connection socket 30 that mateswith a connector of an electrode cable assembly (not shown) tointerconnect the pulse generator 10 with a plurality of intramuscularelectrodes via percutaneous electrode leads. More particularly the cableassembly connected to the socket 30 includes a second connector on adistal end that mates with a connector attached to the proximal end ofeach of the percutaneous stimulation electrode leads and a referenceelectrode lead.

A suitable intramuscular electrode and percutaneous lead are shown inFIG. 2. The electrode lead 40 is fabricated from a 7-strand stainlesssteel wire insulated with a biocompatible polymer. Each individual wirestrand has a diameter of 34 μm and the insulated multi-strand lead wirehas a diameter of 250 μm. The insulated wire is formed into a spiral orhelix as has been found preferred to accommodate high dynamic stressupon muscle flexion and extension, while simultaneously retaining lowsusceptibility to fatigue. The outer diameter of the helically formedelectrode lead 40 is approximately 580 μm and it may be encased orfilled with silicone or the like.

As mentioned above, a proximal end 44 of each of the plurality ofintramuscular electrode lead wires 40 are located exterior to thepatient's body when in use. The proximal end 44 includes a deinsulatedlength for connection to an electrical connector in combination with theremainder of the electrode leads. The distal end 46 of each lead 40,which is inserted directly into muscle tissue, also includes adeinsulated length, which acts as the stimulation electrode 50. It ispreferred that at least a portion of the deinsulated length be bent orotherwise deformed into a barb 48 to anchor the electrode in theselected muscle tissue. A taper 52, made from silicone adhesive or thelike, is formed between the deinsulated distal end 50 and the insulatedportion of the lead 40 to reduce stress concentration.

Unlike surface electrodes which are applied to the surface of thepatient's skin using an adhesive, each of the plurality of percutaneouselectrodes 50 is surgically implanted or inserted into select patientshoulder, arm, or upper-trunk muscle tissue, and the associatedelectrode lead 40 exits the patient percutaneously, i.e., through theskin, for connection to the stimulation pulse generator 10. Preferably,each of the electrodes 50 is implanted or inserted into the selectmuscles by use of a hypodermic needle. Alternatively, or in addition,muscles may be surgically exposed for implantation or minimally invasivetechniques such as arthroscopy may be used. Once all of the electrodesare implanted as desired, their proximal ends are crimped into a commonconnector that mates with the cable assembly which is, in turn,connected to the pulse generator 10 through the connection socket 30. Ofcourse, such therapies or uses may require multiple systems, whichutilize multiple pulse train generators with multiple common connectors.

The present percutaneous, intramuscular stimulation system allows forprecise muscle selection and use of three or more stimulation electrodesand channels. The preferred system in accordance with the presentinvention uses up to eight or more intramuscular electrodes 50, eachconnected to an independent electrode stimulation channel E, and asingle reference electrode 52 which may be either an intramuscular orsurface electrode.

The stimulation pulse generator 10 comprises a microprocessor-basedstimulation pulse generator circuit with a micro controller such as aMotorola 68HC12. Operational instructions or other information arestored in non-volatile storage. Set stimulation therapy or patterns maybe included in this storage. These therapies may be based upongeneralized information such as may be gathered from radiographicevaluation in multiple dimensions along with selected stimulation.Ultimately patient specific information may be incorporated into thestimulation parameters in order to optimize the therapy for a particularindividual application. Preferably, the nonvolatile memory also providesstorage for all patient-specific stimulation protocols. A real timeclock is provided as part of the circuit.

The electrical stimulator current passes between the selected electrodesand the reference electrode. A pulse duration timer provides timinginput PDC as determined by the CPU to the pulse amplitude/durationcontroller to control the duration of each stimulation pulse. Likewise,the CPU provides a pulse amplitude control signal to the circuit by wayof the serial peripheral interface to control the amplitude of eachstimulation pulse. One suitable circuit means for output of stimulationpulses as described above is in accordance with that described in U.S.Pat. No. 5,167,229, the disclosure of which is hereby expresslyincorporated by reference. An impedance detection circuit is used tomonitor the therapy.

Each output channel E1-E8 includes independent electrical charge storagemeans such as a capacitor SC which, is charged to the high voltage VHthrough a respective current limiting diode CD. To generate astimulation pulse, the microcontroller output circuit 102 provideschannel select input data to switch component, as to the particularchannel E1-E8 on which the pulse is to be passed. Switch means SW closesthe selected switch SW1-SW8 accordingly. The microcontroller alsoprovides a pulse amplitude control signal PAC into a voltage-controlledcurrent source VCCS. As such, the pulse amplitude control signal PACcontrols the magnitude of the current I, and the circuit VCCS ensuresthat the current I is constant at that select level as dictated by thepulse amplitude control input PAC. For stimulation of human muscle, itis preferably that the current I be within an approximate range of 1mA-2 OmA.

Upon completion of the cathodic phase Qc as controlled by the pulseduration control signal PDC, the discharged capacitor SC recharges uponopening of the formerly closed one of the switches SW1-SW8. The flow ofrecharging current to the capacitor SC results in a reverse current flowbetween the relevant electrode 50 and the reference electrode 52, thusdefining an anodic pulse phase Qa− The current amplitude in the anodicpulse phase Qa is limited, preferably to 0.5 mA, by the current limitingdiodes CD. Of course, the duration of the anodic phase is determined bythe charging time of the capacitor SC, and current flow is blocked uponthe capacitor becoming fully charged. It should be recognized that theinterval between successive pulses or pulse frequency PF is controlledby the CPU 62 directly through output of the channel select, pulseamplitude, and pulse duration control signals as described at a desiredfrequency PF.

A preferred design implements from 2 to 8 or more independentpreprogrammed patterns. For each pattern, a stimulation session S ispre-programmed into the stimulator circuit by a clinician through use ofthe input means. Each session S has a maximum session duration ofapproximately 9 hours, and a session starting delay D. The maximumsession starting delay D is approximately 1 hour. The session startingdelay D allows a patient to select automatic stimulation session startat some future time. Within each session S, a plurality of stimulationcycles C are programmed for stimulation of selected muscles. Preferably,each stimulation cycle ranges from 2-100 seconds in duration.

With continuing reference to FIG. 3, a stimulus pulse train T includes aplurality of successive stimulus pulses P. As is described above and inthe aforementioned U.S. Pat. No. 5,167,229, each stimulus pulse P iscurrent-regulated and diphasic, i.e., comprises a cathodic charge phaseQc and an anodic charge-phase Qa. The magnitude of the cathodic chargephase Qc, is equal to the magnitude of the anodic charge phase Qa. Thecurrent-regulated, biphasic pulses P provide for consistent musclerecruitment along with minimal tissue damage and electrode corrosion.

Each pulse P is defined by an adjustable pulse amplitude PA and anadjustable pulse duration PD. The pulse frequency PF is also adjustable.Further, the pulse amplitude PA, pulse duration PD, and pulse frequencyPF are independently adjustable for each stimulation channel E. Theamplitude of the anodic charge phase Qa is preferably fixed at 0.5 mA,but may be adjusted if desired.

Pulse “ramping” is used at the beginning and end of each stimulationpulse train T to generate smooth muscle contraction. Ramping is definedherein as the gradual change in cathodic pulse charge magnitude byvarying at least one of the pulse amplitude PA and pulse duration PD. InFIG. 3, the preferred ramping configuration is illustrated in greaterdetail. As mentioned, each of the plurality of stimulationleads/electrodes 40,50 is connected to the pulse generator circuit 60via a stimulation pulse channel E. As illustrated in FIG. 3, eightstimulation pulse channels E1, E2, E8 are provided to independentlydrive up to eight intramuscular electrodes 50. Stimulation pulse trainstransmitted on each channel E1-E8 are transmitted within or inaccordance with a stimulation pulse train envelope B1-B8, respectively.The characteristics of each envelope B1-B8 are independently adjustableby a clinician for each channel E1-E8. Referring particularly to theenvelope B2 for the channel E2, each envelope B1-B8 is defined by adelay or “off” phase PD0 where no pulses are delivered to the electrodeconnected to the subject channel, i.e., the pulses have a pulse durationPD of 0. Thereafter, according to the parameters programmed into thecircuit 60 by a clinician, the pulse duration PD of each pulse P isincreased or “ramped-up” over time during a “ramp-up” phase PD1 from aminimum value (e.g., 5 μlsec) to a programmed maximum value. In a pulseduration “hold” phase PD2, the pulse duration PD remains constant at themaximum programmed value. Finally, during a pulse duration “ramp-down”phase PD3, the pulse duration PD of each pulse P is decreased over timeto lessen the charge delivered to the electrode 50.

This “ramping-up and “ramping-down” is illustrated even further withreference to the stimulation pulse train T which is provided incorrespondence with the envelope B8 of the channel E8. In accordancewith the envelope B8, the pulse P of the pulse train T first graduallyincrease in pulse duration PD, then maintain the maximum pulse durationPD for a select duration, and finally gradually decrease in pulseduration PD.

As mentioned, the pulse amplitude PA, pulse duration PD, pulse frequencyPF, and envelope B1-B8 are user-adjustable for every stimulation channelE, independently of the other channels. Preferably, the stimulationpulse generator circuit 60 is pre-programmed with up to four stimulationpatterns, which will allow a patient to select the prescribed one of thepatterns as required during therapy.

Most preferably, the pulse generator 10 includes at least up to eightstimulation pulse channels E. The stimulation pulse trains T of eachchannel E are sequentially or substantially simultaneously transmittedto their respective electrodes 50. The pulse frequency PF is preferablyadjustable within the range of approximately 5 Hz to approximately 50Hz; the cathodic amplitude PA is preferably adjustable within the rangeof approximately 1 mA to approximately 20 mA; and, the pulse duration PDis preferably adjustable in the range of approximately 5 μsec toapproximately 200 μsec, for a maximum of approximately 250 pulses persecond delivered by the circuit 60.

FIG. 4 illustrates an asynchronous stimulation profile consisting of afirst stimulation cycle 10 administered to a first muscle group, i.e.the posterior deltoid and the supraspinatus, and a second stimulationcycle 20 which has the same stimulation profile but is offset from thefirst cycle and is administered to a second muscle group, i.e. themiddle deltoid in combination with the upper trapezious. This method oftreatment inhibits the misalignment, which might otherwise occur duringthe rest portion of the cycle.

In a further embodiment of the invention, a method of therapy isprovided for treatment of shoulder dysfunction (such as subluxation)which comprises the steps of: 1) percutaneous implantation of two ormore electrodes, so as to contact a muscle or nerve, the electrode beingin electrical communication with a pulse train generator; and 2)actuation of the pulse train generator in accordance with a regiment orprescribed dosage to cause stimulation of the muscle or nerve using theelectrodes which dosage has been defined as a result of a radiographicevaluation in three-dimensions (i.e. from multiple views includinganterior-posterior, lateral) of a shoulder. The regiment or course oftreatment may be a pre-defined course of treatment based on astimulation pattern, which has been stored in a host computer orintegral microprocessor, which can be used to address the pulse traingenerator. Preferably, the regiment will include individual sessionshaving a ramped profile and including intermittent stimulationactivation of the electrode or electrodes with periods of rest.Preferably, the treatment of shoulder subluxation involves implantationof one or more electrodes into the superspinatus as well as into theposterior, middle and anterior deltoids; into the coracolbrachialis;into the biceps and triceps longhead. Even more preferably the treatmentaccounts for shoulder relocation in three dimensions with a focus onstimulation of all heads of the deltoid, the coracobrachialis, thebiceps and the triceps longhead. Modulation of the stimulus may requireprecise muscle activation to balance against agonist and antagonistactivity to avoid undesirable joint translation and rotation.

The preferred treatment regiment is illustrated in FIG. 4 and thustherapy involves two stimulation cycles applied asynchronously. Eachcycle has a 30±10 seconds period with 3-8; preferably 5±1 seconds eachof ramp on and off and 5-15, preferably 10±2 seconds of hold. One cycleis applied to the posterior deltoid in combination with thesupraspinatus while the other cycle is applied at a 5±5 second offset tothe middle deltoid in combination with the upper trapezoidious. Thecycle utilizes a balanced charge wave-form meaning that each pulse hasan equal amount of positive and negative charge in each pulse. Theenvelope illustrates the outline of the amplitude of multiple pulses.The treatment generally involves weekly to daily periods of treatmentfor several minutes up to several hours. One postulated treatmentinvolves 5-480 minutes of treatment, 1-3 times daily for 4-16 weeks. Apreferred dosage us 4-7, preferably 6 hours per day for 6 weeks. Variousmuscles can undergo passive stimulation during the course of the day.The pulse train generator is miniature so that it is easily portable.Further, it provides multiple channels to allow a therapy or treatmentuse involving multiple nerves and/or multiple muscles. It is envisionedthat the method of the present invention may have use in the treatmentof acute and/or chronic dysfunction including the treatment of pain. Forthe treatment of shoulder dysfunction in hemiplegics (i.e., one sidedparalysis) the therapy may even begin immediately upon presentation ofstroke symptoms as a prophalalic treatment with respect to shouldersubluxation. The treatment is envisioned for indications involvingdysfunction of the central nervous systems including stroke or traumaticbrain injury, spinal cord injury, cerebral palsy and other condition,which result in debilitation of the nervous system. The treatment mayincorporate continuous stimulation for some period of time such as fourto eight, or around six hours per day. Since the therapy is passive andrelatively free from pain, the patient may undergo treatment whileotherwise conducting life as usual.

EXAMPLES

In order to assess the clinical feasibility of percutaneous,intramuscular NMES for treating shoulder dysfunction in hemiplegia,three studies were carried out in our laboratory. The first studycompared the level of discomfort associated with intramuscular andtranscutaneous NMES during reduction of shoulder subluxation. The secondstudy was a pilot study investigating the effects of percutaneous,intramuscular NMES on shoulder subluxation, range of motion, pain, motorrecovery and disability in persons with chronic hemiplegia and shouldersubluxation. The third study was a preliminary study to determinewhether the muscles previously selected in the transcutaneous NMESstudies are, in fact, the muscles which provide maximal reduction ofshoulder subluxation.

Example 1

To compare stimulation-induced pain between transcutaneous andpercutaneous, intramuscular NMES, 10 subjects were enrolled withhemiplegia and at least one fingerbreadth of shoulder subluxation. Across over study design was used. Each subject received 3 pairs ofrandomly ordered transcutaneous or intramuscular stimulation. Both typesof stimulation were modulated to provide full joint reduction bypalpation with the least discomfort. Subjects were blinded to the typeof stimulation given. The evaluator was blinded to the type ofstimulation given when assessing joint reduction by palpation and whenadministering the pain measures. Pain was measured using a 10 cm visualanalogue scale and the McGill Pain Questionnaire using the pain ratingindex (PRI) method for quantification of data. The pain descriptors ofthe McGill Pain Questionnaire were read aloud to subjects during eachadministration. Pain measures were obtained immediately after each ofthe six stimulations. After the last pair of stimulations, the subjectswere asked which of the last pair they would prefer for six weeks oftreatment at six hours per day.

The results are summarized in FIGS. 5 and 6. Significantly less pain wasexperienced during percutaneous, intramuscular NMES than duringtranscutaneous NMES. Nine of 10 subjects preferred intramuscular overtranscutaneous stimulation. This study assessed discomfort with twotypes of NMES taking into account two critical factors in studying painwith NMES. First, the stimulation induced pain was measured during theclinical application. Stimulus parameters differ depending on theapplication and may have a significant affect on the discomfortexperienced during stimulation. For example, the current and frequencyrequired for weight bearing activities such as ambulation are muchgreater than those needed for reducing shoulder subluxation. Secondly,the stimulation was administered in the target population. Theperception of pain may potentially be altered based on differences inthe underlying neural pathophysiology. Though these results demonstrateless pain with percutaneous, intramuscular stimulation, they only inferthat treatment with percutaneous, intramuscular NMES is better toleratedthan treatment with transcutaneous NMES.

Example 2

The effects of percutaneous intramuscular NMES was investigated onshoulder subluxation, range of motion, pain, motor recovery anddisability in persons with chronic hemiplegia and shoulder subluxation.In a pre-test, post-test trial, 8 neurologically stable subjectsreceived 6 weeks of intramuscular NMES for 6 hours per day. A pagersized stimulator which could be worn on the belt or placed in a pocketwas designed for this application to allow the subjects to receivetreatment without interfering with mobility and daily activities.Inferior and lateral shoulder subluxation was quantified with anunvalidated radiographic technique. Radiographs of both shoulders wereobtained. The difference in glenohumeral translation between thesubluxated and unaffected shoulder was measured to take into accountnormal variance among individuals. Pain free passive shoulder externalrotation was measured using a hand held goniometer in the supine,relaxed subject, Shoulder pain was quantified using the Brief PainInventory (BPI), which evaluates pain intensity and interference withdaily activities. The BPI has been validated for quantifying cancer painbut has not been validated in hemiplegia or regional shoulder pain.Motor impairment was measured using the upper limb portion of theFugl-Meyer Scale (FMS). The self-care portion of the FunctionalIndependence Measure™ (FIM) was used to evaluate disability. Testing wasperformed prior to administering 6 weeks of intramuscular NMES (T1),after completing the 6-week treatment (T2} and at a 3 month follow-up(T3.) The Wilcoxon Sign Rank Test was used to determine the statisticalsignificance of differences between T1 and T2 and between T2 and 13 forall outcomes. Questionnaires to assess tolerance and ease ofimplementation were developed after the study had begun and wereadministered to half of the users and caregivers.

The results are summarized in FIGS. 7-12. Vertical subluxation, range ofmotion, shoulder pain and self-care skills all improved significantlyfrom pre-treatment to post-treatment. The reduction in joint subluxationwas maintained at 3 months. Shoulder pain increased and range of motiondecreased from post-treatment to the 3-month follow-up but the changeswere not statistically significant. Self-care skills improvednon-significantly from post-treatment to 3-month follow-up. Theself-care portion of the FIM was not a good choice for measurement ofdisability in this population because the self-care tasks can beperformed independently with a single intact upper limb. In this study,improvements in FIM scores may not be due to motor recovery and did notparallel changes in FMS. However, the improved FIM scores may reflectchanges due to other effects of the intervention such as decreased painor confounders such as increased motivation. A trend in improvement ofmotor function was seen after treatment but was only statisticallysignificant at the 3-month follow-up. The median time since onset ofhemiplegia in the subjects studied was 11 months with a range of six to28 months. Though unlikely, some motor improvement may have been due tonatural recovery. Improved FMS were documented in some subjects withflaccid hemiplegia for 2 years or more. Responses to the questionnairesindicated that the treatment was well tolerated, required less than 5minutes per day to don and doff, did not interfere with daily activitiesand was preferred over the use of a sling.

Example 3

The third study determined whether the standard muscles targeted forstimulation provide the best reduction of shoulder subluxation. Thesupraspinatus and posterior deltoid muscles were stimulated in thepreviously discussed transcutaneous NMES studies. These muscles wereselected based on a study by Basmajian et al. In his study, EMG activityin the shoulder muscles of normal adults were observed during rest andinferiorly directed traction on the upper limb. The supraspinatus wasfound to be uniformly active and the posterior deltoid less active underthese conditions. In our pilot experience with intramuscular NMES fortreating shoulder subluxation, the supraspinatus did not consistentlyreduce subluxation during stimulation. A preliminary survey of variousshoulder muscles was undertaken to determine whether other muscles mayprovide better joint reduction during stimulation. Up to 13 shouldermuscles were stimulated in 12 subjects with hemiplegia and at least onefingerbreadth of shoulder subluxation. Muscle selection for testing wasbased on accessibility for implantation of percutaneous electrodes andthe force vectors between the scapula and humueral head generated duringmuscle contraction. The stimulus was titrated to avoid pain and unwantedjoint movement (e.g. active elbow flexion during biceps stimulation).Joint reduction was assessed by palpation in all subjects andradiographically in two subjects using a three-dimensional techniquethat standardizes trunk and limb position, uses the glenoid fossa as areference frame and measures the difference in joint translation betweenthe affected and unaffected shoulders. Stimulation of the supraspinatusmuscle provided incomplete reduction of subluxation. Several othermuscles provided more complete and more consistent joint reductionincluding all heads of the deltoid, the coracobrachialis, the biceps andthe triceps long head. While radiographic inferior subluxationcorrelated well with palpation, the three-dimensional techniquecorrelated poorly with subluxation measured by palpation. Thisdiscrepancy was felt to be due to inadequate assessment of anteriorsubluxation by palpation.

While in accordance with the Patent Statutes the best mode and preferredembodiment have been set forth, the scope of the invention is notlimited thereto but rather by the scope of the attached claims.

1. A method of treating chronic shoulder pain in an individualcomprising: (i) identifying in the individual a site of chronic shoulderpain; (ii) targeting for electrical stimulation a region of shouldermuscle tissue near the site; (iii) providing an electrode that is sizeand configured for insertion into the targeted region of shoulder muscletissue through an introducer without surgical exposure of the shouldermuscle tissue, the electrode including a component to anchor theelectrode in the shoulder muscle tissue, the electrode beingelectrically coupled to an electrode lead that is sized and configuredto extend from the electrode, when inserted into the targeted region ofshoulder muscle tissue, percutaneously through the skin and including aportion that, in use, exits the skin and is exposed outside theindividual; (iv) providing an external electrical stimulation pulsegenerator that is sized an configured, in use, to be carried outside theindividual, the electrical pulse generator including a connector forelectrically coupling to the portion of the electrode lead exposedoutside the individual; (v) inserting the electrode through theintroducer and skin into the targeted region of the shoulder muscletissue without surgical exposure of the shoulder muscle tissue, whereinthe electrode lead extends percutaneously through the skin of theindividual with the section exiting the skin and exposed outside theindividual; (vi) electrically coupling the connector of the externalstimulation pulse generator to the section of the electrode lead exposedoutside the individual; (vii) operating the external stimulation pulsegenerator according to a prescribed treatment regiment to deliverelectrical stimulation pulses to the electrode via the electrode lead tocause contraction of the shoulder muscle tissue at the site; (viii)treating the chronic shoulder pain by (a) temporarily performing (vii)during a prescribed stimulation period of at least one week to achieveby the end of the prescribed stimulation period a statisticallysignificant reduction in the chronic shoulder pain, as measuredaccording to a pain rating index, and (b) terminating (vii) at the endof the prescribed stimulation period to cease delivery of electricalstimulation pulses to the site, wherein no statistically significantincrease in the pain rating index, as measured at the termination of theprescribed stimulation period, occurs at the site for a period of atleast three months after termination of the prescribed stimulationperiod.
 2. A method as defined in claim 1 wherein the prescribedtreatment regiment includes a stimulation pulse train pattern includingat least one stimulation cycle defining a stimulation pulse trainenvelope defined by at least a ramp-up phase of a first select durationin which the pulses of a stimulus pulse train pattern progressivelyincrease in charge, a hold phase of a second select duration in whichthe pulses of the stimulus pulse train pattern are substantiallyconstant charge, and a ramp down phase of a third select duration inwhich the pulses of the stimulus pulse train pattern progressivelydecrease in charge.
 3. A method as defined in claim 1 wherein (ii)includes targeting plural regions of shoulder muscle tissue near thesite of chronic shoulder pain; wherein (iii) includes providing, foreach one of the targeted plural regions, an electrode that is sized andconfigured for insertion into the respective targeted region of shouldermuscle tissue without surgical exposure of the shoulder muscle tissue,the electrode being electrically coupled to an electrode lead that issized and configured to extend from the electrode, when inserted intothe respective targeted region of shoulder muscle tissue, percutaneouslythrough the skin of the individual and including an exposed portionthat, in use, exits the skin outside the individual; wherein (v)comprises inserting one of the electrodes through the skin into each ofthe targeted plural regions of the shoulder muscle tissue; wherein (vi)includes electrically coupling the connector of the external stimulationpulse generator to the exposed section of each electrode lead outsidethe individual; and wherein (vii) includes operating the externalstimulation pulse generator according to the prescribed treatmentregiment to deliver electrical stimulation pulses to the electrodes viathe respective electrode leads to cause contraction of the shouldermuscle tissue.
 4. A method as defined in claim 3 wherein the pluralregions include a first muscle group and a second muscle group.
 5. Amethod as defined in claim 2 wherein the ramp-up phase duration is fromabout 2 to about 8 seconds, the hold phase duration is from about 5 toabout 15 seconds, and the ramp-down phase duration is from about 2 toabout 8 seconds.
 6. A method as defined in claim 5, wherein the ramp-upphase duration is from about 5±1 seconds, the hold phase duration isfrom about 10±2 seconds, and the ramp-down phase duration is from about5±1 seconds.
 7. A method according to claim 1 wherein die electrodecomprises a spiral or helix to accommodate stress due to muscle flexureand/or extension.
 8. A method according to claim 1 wherein the electrodecomprises a component to anchor the electrode in the shoulder muscletissue.
 9. A method according to claim 8 wherein the component comprisesa barb.